A top end Macbook Pro retina really should be capable of sporting a top end 8x series Nvidia as a minimum. In fact a 9x nVidia refresh with 40% the current battery would probably make me drop the cash for another one (I only bought a new Macbook about 3 months ago). I want "this" physical hardware, but with a nice GPU so I can demo things like the Rift DK2 on the road without hulking around another PC laptop just for "those moments". The current Macbook Pro just isn't cut out for modern day 3D like a cheap(ish) MSI stealth Pro is...Trust me Apple... I'll find a power outlet if I need it.
As an aside, it's still the best laptop I've ever owned.
In both machines, I've had faults in with the discrete GPU. Both times required logic board replacements twice. (that's four replacement logic boards across two laptops).
I can absolutely understand why Apple is moving as much as possible of their line to using integrated Intel graphics solutions - they're 'good enough' for the vast majority of people, and have followed Intel's recent energy efficiency work, so not only do they drain the battery slower they produce less heat, and from what I've seen are much less likely to have catastrophic failures than discrete graphics.
If you want discrete graphics, buy a high end machine. If you don't have that requirement, why pay for the extra hardware that is more likely to cause a fault than be of use?